Whitefish Salad on Endive Spears

1/2 cup mayonnaise

1/4 cup minced onion

1 small celery rib, cut into 1/4-inch dice

2 medium radishes, cut into 1/4-inch dice

2 teaspoons fresh lime juice

5 ounces skinless, boneless smoked whitefish, flaked (1 cup)

Freshly ground pepper

24 Belgian endive spears (from 3 endives)

6 cherry or grape tomatoes, quartered